Arrangement for intra-oral X-ray imaging

ABSTRACT

This invention relates to x-ray imaging, especially to an imaging arrangement used in intra-oral x-ray imaging, to a wireless imaging sensor and to a base station for the sensor as well as methods for using the sensor and transmitting the information to the sensor and from the sensor wirelessly, in which invention such a wireless power transmission link is used, which is arranged to be used for supplying at least part of the energy needed by the sensor in connection with the imaging process.

FIELD OF THE INVENTION

The present invention relates to X-ray imaging, especially to an imagingarrangement used in intra-oral X-ray imaging, to a wireless image sensorand a sensor base station pertaining to it, and to methods for using asensor and for transmitting data to and from a sensor wirelessly.

BACKGROUND OF THE INVENTION

Intra-oral X-ray images are taken by using an X-ray examinationapparatus which typically includes, on the one hand, a multi-jointed armconstruction and a radiation source arranged in connection with it and,on the other hand, an image-data receiving means to be positioned withinthe patient's mouth in a desired orientation. Generally, electricimaging sensors, which are based on e.g. charge coupled device (CCD) orcomplementary metal oxide semiconductor (CMOS) technologies, haveincreasingly emerged along with the use of traditional film.

In order to enable electric intra-oral imaging, one should be able to,for the first, supply the operating power required by the sensor to bepositioned within the mouth and, for the second, transfer the image datadetected by the sensor to storage or e.g. onto a display. Furthermore,one must be able to identify in some way the moment of beginning of theimaging at least, i.e., the beginning of irradiation. In the earliestelectric intra-oral X-ray arrangements cords were used not only forsupplying electric energy but also, inter alia, for transmitting signalsfor synchronising operations of the radiation source and the sensor.Since, solutions have been developed in which e.g. the beginning ofirradiation may be identified based on a signal received directly fromthe sensor, whereby the synchronisation of the operations of the sensorand the radiation source via a cable has not been necessary any more.However, the sensor cable was still required for, on the first hand,supplying electric power and, on the other hand, e.g. transmitting imagedata and sensor control information.

In intra-oral X-ray imaging, the sensor has to be repeatedly positionedinto different positions within the patient's mouth. In this context thesensor cord bends, whereby the cord itself and its connection to thesensor are repeatedly subject to such forces, which will readily wearout the cord and especially its connection to the sensor. It is quitetypical that the lifetime of the cord will be shorter than the one ofthe sensor itself. Although in intra-oral imaging arrangements the cordas such may, when arranged to be of suitable length, provide a safetymeans for lessening the possibility of the relatively expensive sensordropping onto the floor and thus getting broken, one has begun in thefield of intra-oral X-ray imaging, as there has been done in many otherfields as well, developing solutions based on wireless technology.

From the viewpoint of the practical realisation of a wireless intra-oralsensor, an essential characteristic of the sensor is its low powerconsumption. As it earlier has been possible to achieve diagnosticallyadequate image quality only with CCD sensor technology, characteristicfeatures of which being fairly high power consumption and complexelectronics—not the least because of the several different voltagelevels required, a wireless intra-oral X-ray arrangement was notpossible to be realised in practice until development of othertechnologies, such as CMOS sensors, had reached a sufficiently highlevel.

A limiting condition of intra-oral X-ray imaging is also the sensor sizewhich cannot, for understandable reasons, be very large both for itssurface area and its thickness. On the first hand, one must be able tosupply in any case the operating power required by the sensor positionedwithin the patient's mouth and, on the other hand, transfer the imageinformation detected by the sensor to a display or for storage. Inaddition, it would be preferable if one would be able to transmit e.g.control signals in the direction of the sensor.

Thus, in the electric intra-oral sensors of the first-generation thetransfer of data and power was realised via cables, as the technologywas not advanced enough for wireless data transmission or, overall, forusing wireless technology. Wireless arrangements developed since aretypically based on using such a base station in which a battery or acapacitor arranged to the sensor is charged either via a physicalelectric connection to be arranged between the base station and thesensor or by means of induction current. Also replaceable batteries maybe used in the sensors. At least a radio frequency (RF) link has beenused for transmitting data from the sensor. As far as these prior artsolutions are concerned, a reference may be made to e.g. specificationU.S. Pat. No. 6,527,442 and Japanese published application 2003-79617.The latter of these, for example, describes an imaging arrangementintended to be used in intra-oral X-ray imaging in which a battery or arechargeable battery, used as the power source of the sensor, is placedin a holder unit outside the sensor, which holder unit is connected tothe sensor via a cord. The rechargeable battery may be charged in thebase station of the holder unit. Image data may be transmitted from thesensor via the holder unit either when it is connected to its basestation or wirelessly by radio technology. The wireless datatransmission may be arranged either between the sensor and the basestation, or to occur directly together with a personal computer e.g. byBluetooth technology. If the battery can be realised small enough, itmay be placed within the sensor, too.

Wireless digital intra-oral sensors on the market today have certaincharacteristics which would be nice to get rid of or be able to beimproved. For the first, using batteries as power source of the sensorcauses, besides the bother and cost of changing the battery from time totime, also the fact that it is almost impossible, in practice, toarrange the sensor hermetically sealable in order to enable itscold-sterilisation (immersing it into a liquid). For the second, whenusing e.g. a rechargeable battery or a capacitor, they must be regularlyre-charged before an imaging event, or between them. Here one may findoneself in situations in which charging up must be waited for—especiallywhen the imaging arrangement should, for reasons of radiation hygiene tobegin with, be realised such that the imaging cannot be initiated even,if it is possible that the energy stored in the sensor is not enough forbeing certain that the picture can be taken and either saved in thesensor itself or sent forward.

The small sensor size required in intra-oral imaging is problematic alsofrom the viewpoint of wireless data transmission, because RF linksrealisable with current technology that would enable quick enoughtransmission of image information and especially bidirectional datatransmission are relatively large and require reasonably much power.Using bidirectional RF links also requisites reasonably complicatedelectronics. On the other hand, if data transmission from the sensor isarranged only unidirectional, e.g. by sending image information from thesensor to the receiver in real time, re-transmitting the image is notpossible in case needed but one has to simply trust that there are nodisturbances in the data transmission. In data transmission realised byradio frequencies, disturbances may be caused by e.g. the lengthy datatransmission distance from the sensor in the patient's mouth (throughsoft tissue) to the receiver and both GSM phones and other radiotransmitters operating at high frequencies (>10 MHz) (Bluetooth, WLAN)or other radio-frequency devices of high-power. In case the power of thepower source is not, for some reason, sufficient for performing theimaging event as a whole and transmission of image data is only possiblein real time, one may have to repeat the whole imaging.

There may be a need to use a plurality of sensors in the same premises.When using radio frequencies, one might have to use e.g. differentfrequencies or one has to arrange selectable transmission channels tothe sensors for realising undisturbed data transmission. Even then onemust in any case be able to manage in some manner which frequency orchannel can be used at a given time.

An object of the present invention, with its preferable embodiments, isthus to offer possibilities for decreasing or avoiding many of theabove-described problems and limitations. Especially, an object of theinvention is to decrease the problems related to wireless intra-oralimaging based on use of batteries, on one hand, and on sensors to becharged beforehand for imaging, on the other.

BRIEF DESCRIPTION OF THE INVENTION

The essential characteristics of the invention are presented in theaccompanying patent claims. In the different embodiments of theinvention there is no need to charge the image sensor to be ready forimaging beforehand, as energy may be supplied to it, in case need be, inconnection with the actual imaging event. The sensor is arranged to beused without a physical contact to any electric power or datatransmission bus and e.g. to be activated when it is brought to theoperating range of a wireless power transmitter. Preferably, thetransmitter sending energy wirelessly to the sensor is integrated withe.g. the source of radiation, whereby when the corresponding receiver islocated in the sensor, the arrangement may be realised e.g. in such away that irradiation is possible only when the sensor is located withinthe operating range of the power transmission link in question, whichrange is arranged short.

The invention with its preferable embodiments will facilitate the workstages of the dental care personnel external to the actual imaging, asone does not have to take care of changing batteries nor charging thesensor beforehand prior to the imaging event.

It is possible to realise an intra-oral sensor according to theinvention without any lids or slots as hermetically sealed, whichenables its sterilisation by immersing in the sterilising liquid, too.

The imaging arrangement may preferably be realised so that an inductivetransmitter is used in power transmission, which transmitter may also beused for supplying data to the sensor. It is also possible to utilisethe magnetic field produced by the transmitter of the inductive link inpositioning the sensor to a desired position with respect to the X-raybeam produced by the radiation source.

If the sensor is arranged to be operable only in the essential proximityof the power transmitter one may use such an RF link for transmission ofimage data from the sensor in which the power of the transmitter isconsiderably low. Further one may accomplish a good immunity againstdisturbances caused by other devices, such as GSM phones, by usingdirectional antennas and by arranging the receiver of the RF link quiteinsensitive and/or by placing it inside a beam limiter (of metal) of theX-ray source. Thus, an embodiment of the invention enables a solution inwhich the data transmission may operate reliably in different operatingconditions and more than one sensor may be used within the same spacewithout them necessarily disturbing each other's operation.

The invention also enables implementation of the sensor in a relativelysmall size but, despite of that, as capable of receiving and sendinginformation wirelessly in its imaging position, i.e., to communicatebidirectionally.

Other objects and some preferable embodiments of the invention will bedescribed in the following in more detail with the aid of theaccompanying figures as well. In the following and in the above, whenusing terms “energy” and “power” in the context of this application ismeant, in practice, the same thing, i.e., the “energy” or the “operatingpower” which must be available for the sensor in connection with theimaging event for enabling imaging.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2 a and 2 b show a typical intra-oral X-ray device.

FIG. 3 shows components of a sensor and its base station suitable to beused in the imaging arrangement according to the invention.

FIGS. 4 a and 4 b show an arrangement according to the invention forrealising transmission links.

FIGS. 5 and 6 show embodiments according to the invention of methods forsupplying operating power to the intra-oral sensor in connection with animaging event.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1, 2 a and 2 b show a typical intra-oral X-ray device (1) whichincludes a control panel (2), a jointed arm construction (3) and anX-ray source (4). FIG. 2 b shows additionally an elongated collimator(4′) which may be attached to a housing of the X-ray source (4) forlimiting the X-ray beam more precisely and thus minimising the radiationdose received by the patient. The multi-element arm-joint constructions(3) of intra-oral X-ray devices create a lot of degrees of freedom forpositioning the X-ray source (4) in a desired manner.

FIG. 3 shows components of a sensor (30) and a base station (40)suitable to be used in the imaging arrangement according to theinvention. FIGS. 4 a and 4 b illustrate, for their part, by means ofexamples how transmission links (33, 43; 36, 46) used in the inventionand shown in FIG. 3 may be arranged to an intra-oral X-ray device (1)according to FIGS. 1, 2 a and 2 b.

The sensor (30) according to FIG. 3 includes an FPGA (field programmablegate array) or an ASIC (application specific integrated circuit) circuit(31) controlling its different functions and a CMOS detector (32).Energy may be supplied to the sensor (30) via a wireless transmissionlink (33, 43), which in the embodiment according to FIG. 3 comprises, onthe side of the sensor (30), a receiver (33) of an inductive-linkincluding a coil (34). The coil (34) of the inductive receiver (33) maybe arranged e.g. as in the shape of a rectangle so that it essentiallyimitates the shape of the sensor (30) perimeter and is located in theessential proximity of at least part of the sensor (30) edges. The coil(34) is preferably arranged in connection with the sensor housing sothat the winding will not limit the active detector surface available inthe sensor. The receiver (33) to be arranged to the sensor may also bee.g. an RF receiver or other corresponding component receiving energywirelessly and not being electrically chargeable.

The power supply circuit (35) as such belonging to the sensor (30) mayinclude e.g. a chargeable capacitor, or e.g. a rechargeable battery, butthe sensor may be realised also in a way that it does not include anysuch component which could be used for storing energy supplied to thesensor (30) beforehand for enabling its use without the “on-line powersupply” performed in connection with the imaging event via the wirelesstransmission link (33, 43). The receiver of the transmission-link (33)arranged to the sensor (30) is therefore either the primary power sourcesupplying current to the sensor electronics, whereby the energy storingcapacity of the components possibly belonging to the power supplycircuit (35) being capable of storing energy may also be lower than theelectric power required by the sensor electronics in connection with anindividual imaging event, or it may function as transmitter of theenergy to be supplied to the sensor (30), e.g. to the capacitorfunctioning as a primary power source. Then, the sensor electronics mayinclude a means for identifying the charge level of a capacitor or othercomponent capable of storing energy, and for sending a signal of theneed of additional energy e.g. when a preset limit value has been passedunder—and on the other hand, correspondingly, a means for sending asignal of charging up or e.g. of that a preset minimum charge level hasbeen reached, such as one being adequate for performing a single imagingevent.

The detector (32) used in the sensor (30) may be monolithic and at leastpart of the actual sensor electronics may be integrated with it so thatalready the output from the detector is e.g. in 12-bit digital form.Even though part of the active detector area will be lost as aconsequence of such increase of electronics, the loss may be minimisedby arranging the main portion of the components to one end of thedetector (32) and to the other three sides only that portion of theelectronics which is necessary. In case CMOS technology is used, thepower requirement of the sensor (30) is relatively low. With advancingtechnology, it is presumable that one will be able to integrate thewhole FPGA or ASIC circuit (31) with the detector (32). On the otherhand, with advancing detector technology it is presumable that a sensorwith such preferable characteristics which are presented as advantagesof the CMOS technology here when using it in an application according tothis invention will be realisable also with other solutions than theones based on CMOS technology.

Image information is transmitted from the sensor according to FIG. 3 byan RF transmitter (36) of 2.4 GHz, either essentially in real time asimage data is detected on the detector (32) (so-called streaming mode)or essentially immediately after the image has been taken. It ispossible to arrange e.g. a RAM (random access memory) or a FLASH memory(38) to the sensor (30) for temporarily storing the detected image,whereby it can also be re-sent in case need be. The size of the memorymay be arranged to enable storing of either the image data as a whole oronly part of it. In the latter case, the imaging arrangement ispreferably implemented so that there has been arranged a means to thebase station (40) for identifying the data packets possibly damaged intransmission and a means for transmitting information of this quickly tothe sensor (30). This is possible e.g. by using the energy transmissionlink (33, 43) for this data transmission and by arranging the speed ofit to be sufficient. In even more general terms, thus, the energytransmission link (33, 43) may be used for transmitting to the sensor(30) both energy and information.

FIG. 3 shows also a preferable solution for a base station (40)according to the invention. In the context of this invention, a basestation means primarily a functional entity which may be arranged notonly as a single physical unit, but its components or part thereof mayalso be integrated partly or completely with other construction(s) ordevice(s), such as a radiation source or an image processing device.Energy needed for operating a sensor (30) in connection with an imagingevent may be transmitted to it via the inductive transmitter (43) of thebase station (40) shown in FIG. 3. As already referred to above, theinductive link (33, 43) may also be used for data transmission in thedirection of the sensor (30). Then again data, such as image and statusinformation that has been transmitted by the sensor (30) will bereceived at the RF receiver (46) arranged to the base station (40). Byarranging to the imaging arrangement bidirectional data transmissionaccording to FIG. 3 by means of, first, an unidirectional RF link (36,46), and second, an inductive link (33, 43) one will be able to useunidirectional RF links which are considerably smaller and simpler thanbidirectional RF links that, for its part, enhances possibilities forrealising the sensor (30) as small in size.

It is possible to implement the invention so that significantly lowerdata transmission speed is used for sending control data to the sensor(30) than what is required in practice for transmitting image data fromthe sensor (30), but also e.g. an inductive link (33, 43) may berealised such that also a high-speed data transmission is enabled. Then,it can be utilised e.g. in the above-described manner for transmittingerror messages to the sensor (30) while image data is being transmittedin a situation in which one of the transmitted data packets has beendamaged. Data transmission errors are actually not a real problem whensuch a large memory (37) is arranged to the sensor (30) that the wholeimage data may be re-transmitted in case needed, but by arranging thedata transmission connections such that information of the damaged datapacket will be transmitted to the sensor (30) in time, in view ofenabling re-transmission of the data packet still in the memory (38), itis sufficient to use also a smaller memory.

The base station (40) according to FIG. 3 also includes a base-stationpower supply circuit (45), an FPGA circuit (41) transmitting image datato the processor (49) of the base-station and a memory (48) functioningin connection with the processor, which memory enables temporary storingof image-data received from the sensor (30). In addition, there has beenarranged Ethernet and/or USB (Universal Serial Bus) user interfaces (61,62) to the base station (40) via which one is able to connect e.g. to animage processing device, a patient management system of a dental clinicetc. connected to a local area network. Furthermore, the base stationmay be arranged with a data transmission connection, not shown in FIG.3, via which the operation of the radiation source (4) and the sensor(30) may be synchronised, if so desired, such that the control system ofthe imaging arrangement is arranged to prevent use of the radiationsource (4) unless the sensor (30) used in imaging is located within theoperating range of the power transmission link (33, 43). Yet a means maybe arranged to the sensor electronics for identifying the presence ofthe receiver (33) of the power transmission link (33, 43) within theoperating range of the power transmission link, and a means foractivating the sensor to be ready for imaging as a response to saididentification. Then, the sensor (30) may be used, i.e., it is ready toreceive radiation including image information only when the sensor (30)is located within the operating range of the power transmission link(33, 43), irrespective of the charge level of a component capable ofstoring energy possibly arranged to it. Naturally, the components of abase station (40) according to or corresponding to that of FIG. 3, orpart thereof may also be e.g. an integrated part of electronics of aradiation source (4) or be divided physically to even more than oneunit.

In the arrangement according to the invention, the base station (40) maytake the power it requires from the bus (Power-LAN, USB) via which imagedata is transmitted forward to a personal computer (PC) or a datanetwork, whereby one avoids using an external power source needed forthis purpose only. There may be circumstances, though, in which such apreferable and simple solution is not adequate, in light of which thebase station (40) may be provided with a connection of its own for anexternal power source.

FIGS. 4 a and 4 b, especially FIG. 4 a, illustrate one preferableembodiment of the invention in which the coil (44) of the inductivetransmitter (43) and the RF receiver (46) together with its antenna (47)have been physically separated from the actual base station (40) to forman adapter or a transponder (70) of e.g. circular or rectangular formand being connectable to the X-ray source (4), e.g. to a collimator (4′)attached thereto, and being connected to the electronics of the actualbase station (40) via a cord (71). The RF receiver (46) with its antenna(47) shown in FIG. 4 a has been left out of FIG. 4 b for simplicity'ssake, and FIG. 4 b has been correspondingly complemented compared toFIG. 4 a to show also how the sensor (30) would be typically positionedin connection with an imaging event with respect to the transponder (70)according to FIG. 4 a. So, if also the sensor (30) and e.g. thecollimator (4′) of the radiation source (4) were drawn in FIG. 4 a, thesensor (30) would be located to the left of the transponder (70) and thecollimator (4′) would converge to the transponder (70) from the right.

In the embodiment according to FIGS. 4 a and 4 b the coil (44) of theinductive transmitter (43) is thus arranged within a ring-shaped adapteror transponder (70), and also the antenna (47) of the RF receiver (46)and its preamplifier (not shown in the figures) are integrated with theadapter (70). The adapter (70) may be attached to the end of e.g. anX-ray tube head (4) or a collimator tube (4′) used in it. In such anarrangement, the transmission links (33, 43; 36, 46) will always becomepositioned to roughly the same distance, such as around 2-8 cm, and inthe same direction with respect to each other in connection with imagingwhen the imaging arrangement (50) is ready for imaging, i.e., when theintra-oral sensor (30) is positioned in the patient's mouth and theX-ray source (4) is located in its corresponding imaging position. Interalia, in such embodiment of the invention, one is able to usedirectional antennas (37, 47) for transmitting image data which, for itspart, improves noise immunity of the data transmission system. It isalso possible to place the antenna (47) of the RF receiver inside thecollimator tube (4′) in order to protect it from external sources ofdisturbances. When, in addition, the distance of data transmissionbetween the RF link (36, 46) antennas (37, 47) will therefore be short,the transmission power it requires will also be low. The datatransmission distance is thus in practise e.g. less than 15 cm, such asin the order of 2-8 cm. It is possible to arrange the RF receiver (46)receiving image information less sensitive and thus make the datatransmission relatively immune to the effects of possible sources ofdisturbances. The short transmission distance also enables thatinterference will not be created from the other sensors possibly beingin use and thus there is no need to code the sensors to differentchannels.

Concerning the energy transmission, the intra-oral X-ray imagingarrangement according to the invention is preferably realised such thatin connection with the imaging situation the transmitter (43) supplyingenergy to the sensor (30) is arranged to always become positioned in theessential vicinity of the sensor (30) positioned in the patient's mouth.Such positioning objects are e.g. a holder arranged on the patient'sneck, ear or a band on his/her forehead or a corresponding item, or e.g.on the headrest of the dental chair or, as said, the X-ray source (4)itself.

In connection with intra-oral X-ray imaging one typically aims tocollimate (limit) the X-ray beam to correspond the shape and size of theimage-data receiver used and to position the image-data receiver at thecentre of the beam; this situation being illustrated also in FIG. 4 b.One preferable embodiment of the invention thus comprises an arrangementin which the inductive transmitter is placed within the X-ray source andin which small receiver coils are arranged e.g. essentially to thecorners of a sensor (30) of essentially of rectangular shape, or to atleast one of them. When the sensor (30) is being positioned with respectto the radiation source (4)—or in connection with intra-oral imaging,more frequently perhaps vice versa, when the X-ray source is beingpositioned with respect to the sensor—the signals received from thecoils change according to how their position changes in the magneticfield produced by the inductive transmitter (43) attached to the X-raysource (4). These signals may be arranged to be sent e.g. via the RFlink (36, 46) as signals indicating the relative positions of the sensor(30) and the X-ray source (4), which signals may be utilised inachieving the desired relative position of the sensor (30) and theradiation source (4). Naturally, it is possible to receive more datafrom several of such coils compared to only one coil. However, it ispossible to arrange a corresponding signal from a receiver (33) of theinductive link (33, 43) only, which receiver essentially circles theedges of the sensor (30), whereby even it alone can be used tofacilitate in positioning of the sensor.

The wireless data transfer of intra-oral imaging may thus be realised sothat e.g. a sensor including a CMOS detector will communicate wirelesslybidirectionally with a base station into which base station, or intofunctional connection thereof is also arranged a means for wirelessenergy transmission. When in connection with imaging a transmittersupplying energy and a sensor comprising a corresponding receiver arebrought within the operating range of the link formed by them,preferably into the essential vicinity of each other, such as within anoperating range arranged to be of less than 50 cm, preferably less than15 cm, such as 2-8 cm, it is possible to supply the sensor with energyin connection with the imaging event, whereby imaging is always possibleirrespective of the charge level of the component capable of storingenergy possibly pertaining to the sensor when starting the imaging. Inthis arrangement, it is thus always possible to use the sensor when itis located substantially close to the transmitter of the energytransmission link. Operating power is preferably transmitted to thesensor inductively, whereby the inductive transmitter is preferablyplaced e.g. in connection with the end of the intra-oral X-ray tubehead, e.g. to the tube-like part of its housing, or to the adapter to bepositioned at the end of the collimator connected to it. The inductivetransmitter may also be integrated e.g. as a part of the construction ofthe X-ray source.

The imaging arrangement may be realised so that use of the sensor is notpossible elsewhere but within operating range of the power transmissionlink, whereby in connection with the imaging event the operating systemof the imaging arrangement is arranged to identify when the sensor isbrought into the operating range of the power transmission link and theimaging may be started. The field of inductive power transmission may bearranged to be of relatively low frequency for minimising the possibledisturbing effects it may have to the operation of the imaging sensor.The frequency used in the transmission may be e.g. essentially lowerthan 500 kHz, even totally of a different order of magnitude.

The arrangement may also be implemented such that importing of energy tothe sensor during an imaging event may be controlled. The arrangementmay be realized e.g. such that the energy feed may be kept shut downe.g. during the actual exposure, while reading image data from thedetector to a memory possibly arranged to the sensor, or when sending itfrom the sensor to the ether. The power of the energy transmission linkmay be arranged lower than the power taken by the (RF) transmitter linkused in transmitting image data. An interruption of the energytransmission may have an enhancing effect in that the power transmissiontaking place during an imaging event will not cause disturbances to theoperation of the sensor. A means may be arranged to the sensor itself,too, for adjusting its power consumption at different stages of theimaging event.

Thus, according to one embodiment of the invention, it is possible tostore the image data detected by the detector temporarily to a memoryarranged to the sensor and to transmit it for storage from the detectorafter the exposure has finished, preferably as quickly as possible. Thismay be realised e.g. in such an arrangement in which the time theirradiation ends is known beforehand or it is identified. However, it ispossible to read the signal of particularly e.g. a CMOS-type detectorcontinuously also during the exposure. The sensor may then be arrangedusable also in the so-called streaming mode, i.e., so that image data istransmitted from the sensor continuously during exposure. It will thenbe later possible to detect the beginning and the end of the exposure bysoftware e.g. from the signal stored in the PC's memory. When image datais transmitted in real time at the same rate as it is read, e.g. at 300ms intervals, there is no need to know the maximum exposure time fromthe viewpoint of image formation, when the data possibly causingoverexposure may simply be ignored in image processing.

All in all, according to the invention, sensor may be supplied withenergy in connection with the imaging event whereby it will always beready to be used for imaging, irrespective of what the charge level ofthe component capable of storing energy possibly arranged theretohappens to be upon initiating the imaging. An indication light or othersignal may be arranged in connection with the inductive transmitter,such as to the intra-oral X-ray source in the embodiment according toFIG. 4 b, which signal will indicate after the imaging that transmissionof image information has been completed. When using a sensor providedwith memory, it is naturally also possible to stop the transmission ofthe data, to do it later after imaging and/or transmit the data morethan once in case the data transmission has in some way or anotherfailed. Considering subsequent data transmission, it is possible toarrange a holder e.g. in connection with the X-ray tube, to which thesensor may be placed after imaging to enable communication with the basestation arranged to the X-ray tube still after the actual imaging. Intransmitting data from the sensor, a high-frequency radio transmitterand e.g. transmit power of the order of less than 1 mW are preferablyused for minimising the effect of transmission on the operations of theCMOS detector and the digital electronics of the sensor.

FIGS. 5 and 6 show two examples of how the invention may be applied inpractise in connection with intra-oral X-ray imaging. FIG. 5 shows theuse of the invention in a manner in which mutual operation of theradiation source and the energy transmission link have beensynchronised. According to this embodiment, in the first stage whenpower of the X-ray source is turned on, the arrangement enters a STANDBY mode. The preparation stage of the imaging may include, inter alia,at least initial positioning of the radiation source, the object to beimaged and the sensor, ready for imaging. Then, when upon initiating theactual imaging an irradiation start signal is given from the exposureswitch of the radiation source, the system first activates thetransmitter of the energy transmission link according to the inventionand checks if there is such a sensor unit within the operation range ofthe link which the system recognises. (As all sensors are individualsand their use requires knowledge of the sensor-specific calibrationdata, it is possible to use in the imaging only such sensors the repair(calibration) file of which is stored to a database pertaining to theimaging arrangement in order that one will be able to form from theimage data detected by particularly that sensor in question a “real”image representing the object. With an individual serial number, it isalso possible to prevent an unauthorised use of the sensor and makestealing of it pointless by user-specific opening code.) In practice,the identification of the sensor takes place so that, when being locatedwithin the operating range of the energy transmission link, the sensorsends a signal including its individual identifier via a datatransmission link pertaining to the arrangement as a response to itsactivation. If the identifier in question is not stored to the system,i.e., if one tries to use such a sensor the databases used by theimaging arrangement do not identify, or if e.g. the respective distancebetween transmitter and receiver of the power-transmission-link isgreater than the operating range of the link, or if the charge level ofthe possible component of the sensor capable of storing energy is toolow, or if the system detects some other error in the imagingarrangement, irradiation does not start and the system gives an errorsignal, such as a sound signal, and informs of the cause of the error. Acause of the error signal may also be e.g. inaccurate positioning of thesensor with respect to the X-ray beam produced by the radiation source.

When preconditions for a successful imaging exist, then e.g. theEXPOSURE light belonging to the arrangement is turned on, and if noexposure automatics for the imaging are included in the arrangement,irradiation of a preset duration starts. After the irradiation, theEXPOSURE light is turned off. After the exposure, the arrangement maystill enter a separate BUSY mode the duration of which may depend on,for example, how transfer of the image data detected by the detectorelement is arranged to occur, i.e., if there is arranged a memory to thesensor via which the transfer may be done partially or as a whole alsoafter the exposure, if there has been arranged, in connection with thetransfer, feedback to transmit to the sensor information regarding datapackets that may have been damaged etc. The transfer of image data maythus also be realised so that the data detected by the detector is firststored to a memory in the detector, after the imaging the sensor istransferred e.g. to a holder arranged in connection with the basestation, i.e., to a position in which it is within the operating rangeof the power transmission link, and image data is transmitted from thesensor only at this stage. After transfer of the image data, indicationlights turn off, the energy transmission link inactivates and the systemreturns to the STAND BY mode.

FIG. 6 shows an example of an embodiment in which the energytransmission link and the radiation source function independently withrespect to each other. In this solution, the base station of the energytransmission link communicates with e.g. a PC, and when being in theSTAND BY mode, the transmitter of the energy transmission linkperiodically sends short pulses to the ether, whereby as a response tothe signal of finding a sensor within the operating range of thearrangement, the operation mode of the transmitter changes from saidperiodical-pulse-sending mode to an actual READY mode and the sensor isactivated ready for imaging. For the sake of simplicity, in the diagramaccording to FIG. 6 the alternative that one would try to use some othersensor individual than such known by the system, and also other possibleerror situations shown in connection with the embodiment according toFIG. 5, have been omitted. If no actual exposure is done e.g. within atime preset to the system from the time the system went to the READYmode, that is, i.e., if no signal will be received from the sensorwithin such time of the start of irradiation, the system returns to theSTAND BY mode as described above. Such a situation may occur e.g. whenan exceptionally long time elapses for positioning of the sensor and theradiation source for imaging.

Detecting the start of irradiation causes a change of the status of thesystem to an EXPOSURE mode, during which the information detected by thedetector will be integrated e.g. for a pre-determined time or until theend of irradiation is detected. If the arrangement is implemented sothat the data detected by the detector is read by short intervalscontinuously from the detector already during the exposure, thedetection of the end of irradiation may be based on an observation of asudden fall of the detected signal level. The transmission of image datafrom the sensor may also be realised e.g. in some manner presented abovein connection with the description of FIG. 5, after which the EXPOSURE(or BUSY) indication light is turned off and the arrangement returns tothe STAND BY mode.

The invention is described here particularly in connection with itsprimarily preferred application, intra-oral X-ray imaging. In principle,it is possible to supply the sensor with operating power with some otherwireless technology than inductively as according to the embodimentsdescribed above, and in principle, by using only one link fortransmitting both energy (and data) to the direction of the sensor and,on the other hand, for transmitting image data from the sensor. However,an arrangement according to the above-described embodiments, in whichenergy is supplied to the sensor inductively and image data istransmitted in radio frequencies, respectively, enables an energytransmission/bidirectional data transmission assembly exquisitelyapplicable for intra-oral imaging. Then, it is also possible toconstruct the imaging arrangement such that the magnetic field formed bythe power transmission link may also be utilised in positioning thesensor with respect to the X-ray source, as described above.

According to one preferable embodiment of the invention, the sensor datatransmission is thus bidirectional and realised e.g. so that image andstatus data is sent from the sensor with high rate (such as at least 10Mbit/s) with an essentially high-frequency RF transmission link of e.g.2.4 GHz, and the sensor receives energy inductively, whereby theinductive link may also be used for slower (such as less than 9,600kbit/s) communication in the direction of the sensor, such as forsending the sensor control signals.

A sensor according to the invention may be implemented without anycomponents which would be large in size, wear out when used or age or bereplaceable, such as batteries or rechargeable batteries, whereby itslifetime will be long. Actually, almost the only possibility for such asensor getting broken is a mechanical breakage caused by too a highexternal mechanical strains, such as a physical impact caused by thesensor dropping onto the floor or a physical impact caused by anothercorresponding accident. The risk of dropping onto the floor may beprevented by e.g. a safety cord and a small lug arranged to the backcover of the sensor or by other corresponding fastener arrangement. Ifone uses a string manufactured of thin Kevlar fibre or nylon line it canbe cold-sterilised together with the sensor, or one may use disposablestrings. Then, it is not necessary to use the protective bags typicallyused for hygienic reasons with a sensor according to the invention.

Thus, the arrangements according to the invention and its preferableembodiments provide new kinds of possibilities for implementing awireless intra-oral sensor. For example, the use of a high-frequency andunidirectional RF link for data transmission enables a simpler sensorconstruction which can be realised smaller in size and the control ofwhich is also notably simple. Because of the short transmission range,also the power consumption of the data transmission link is low, wherebyalso the amount of power required by the sensor is low. The use of shorttransmission range and a high-frequency data transmission link enablerealisation of the invention without sophisticated uniqueapplication-specific arrangements, by using prior art solutions whichhave proven to be functional. It is also possible to arrange the datatransmission channel as relatively immune to external disturbances. Thecomponents of the RF link may be realised either with discrete parts oras an integrated circuit, the use of neither disturbing the inductivelink of the other direction pertaining to the arrangement when the linksuse essentially different frequency bands. If desired, the image datamay be transmitted in real time.

The sensor to be used in imaging may be implemented according to theinvention as small in size, as the energy required for using the sensormay be transmitted to the sensor in part or completely in connectionwith the imaging event. Thus, if a component capable of storing energyshould be wished to be arranged in the sensor, it may nevertheless beimplemented as small in size. The sensor needs not to be chargedbeforehand in order for it to be ready for use and it may be realizedwithout a battery or other, changeable or maintenance-requiringcomponent, whereby it can be arranged as hermetically housed andgalvanically insulated, which allows for cold-sterilisation of thesensor between imaging of different patients.

It is well known for a man skilled in the art that the present inventionmay be realised within the scope of protection defined by theaccompanying patent claims also according to other embodiments than theones presented above, inter alia, along with new possibilities offeredby the advancement of detector technology.

1. An intra-oral X-ray imaging arrangement, which includes a controlsystem, a radiation source which is arranged in connection with ajointed arm construction, a sensor and a wireless image datatransmission link for transmitting at least image data detected by thesensor to a device other than said sensor, a transmitter of said imagedata transmission link being arranged in connection with the sensor, anda receiver of said image data transmission link at least in functionalconnection with said device other than the sensor, wherein the imagingarrangement further includes a wireless power transmission link or saidimage data transmission link is arranged to function also as a wirelesspower transmission link, and wherein said control system of the imagingarrangement is arranged to supply the sensor with energy via said powertransmission link or via said image data transmission link functioningas a power transmission link in connection with an imaging event andwherein the arrangement includes a means for transmitting a signal fromthe sensor as a response to the sensor and a transmitter of the powertransmission link, being located within the operating range of the powertransmission link, and a means for synchronising the operations of saidpower transmission link and radiation source (i) so that irradiationcannot be started if the control system of the imaging arrangement hasno information on the receiver of the power transmission link arrangedto the sensor being located within the operating range of the powertransmission link or (ii) so that irradiation cannot be started before asignal has been received from the sensor that its charge level issufficient according to a pre-set limit value in view of the powertransmission speed used for performing at least one imaging event.
 2. Animaging arrangement according to claim 1, wherein said receiver of thepower transmission link pertains to sensor electronics, said receiver ofthe power transmission link being either a primary power source of apower supply circuit pertaining to the sensor electronics or a componenttransmitting energy to a component belonging to the sensor electronicsbeing capable of storing energy.
 3. An imaging arrangement according toclaim 1, wherein said imaging arrangement includes a means fortransmitting to the sensor energy wirelessly during the actual imagingevent.
 4. An imaging arrangement according to claim 1, wherein sensorelectronics includes a component or components capable of storingenergy, and wherein a total energy storing capacity the component orcomponents pertaining to the sensor electronics that are capable ofstoring energy is lower than energy required by the sensor in connectionwith an individual imaging event.
 5. An imaging arrangement according toclaim 1, wherein the operation range of said power transmission link isarranged to be under 50 cm.
 6. An imaging arrangement according to claim1, wherein the transmitter of said power transmission link is placed orarranged to be placed in a location or a position in which, when anobject to be imaged and said sensor are positioned to their imagingpositions according to the imaging arrangement, the sensor is positionedwithin the operating range of the power transmission link.
 7. An imagingarrangement according to claim 6, wherein the transmitter of the powertransmission link is arranged to be placed to the radiation source or toa base station arranged in essential connection with the radiationsource or to a base station attachable to a patient or arranged to aheadrest of a dental chair.
 8. An imaging arrangement according to claim1, wherein said control system includes a control means arranged tocontrol power transmitted to the sensor during an imaging event and/orarranged to control power used by the sensor during an imaging event. 9.An imaging arrangement according to claim 1, which arrangement includesa transmission means for bidirectionally transmitting data between thesensor and the control system of the imaging arrangement, which datacomprises at least control commands and image data detected by thesensor, or wherein said power transmission link is arranged to transmitduring the imaging event both energy required by the sensor and controlsignals for the sensor.
 10. An imaging arrangement according to claim 9,wherein said power transmission link is an inductive link and thereceiver of said inductive link comprises a coil essentially imitatingthe shape of the sensor perimeter and being located at least in part inan essential vicinity of edges of the sensor.
 11. An imaging arrangementaccording to claim 1, wherein said wireless image data transmission linktransmitting at least the image data detected by the sensor is aunidirectional RF link or a high-frequency RF link or an RF link inwhich directional antennas are used.
 12. A method for using an x-rayimaging sensor, which x-ray imaging sensor comprises a sensor housingand sensor electronics arranged therein, and in which method for usingthe x-ray imaging sensor, an imaging arrangement is used in which allthe energy required for using the x-ray imaging sensor is taken from anenergy source arranged in connection with the x-ray imaging sensor,wherein, a receiver of a wireless transmission link is used, at leastpartly, as said energy source so that said wireless transmission link isarranged to function at least as a wireless power transmission link bysupplying the x-ray imaging sensor with energy said x-ray imaging sensorrequires via said wireless power transmission link in connection with animaging event and wherein the x-ray imaging sensor is arranged to becomeactivated in connection with the imaging event as a response to a signalwhich indicates that the transmitter and the receiver of said powertransmission link have been brought within an operating range of thetransmission link, which signal is created so that, before a start ofthe imaging event the transmitter of said power transmission link is setto a STAND BY mode, where-upon it starts to periodically send signalpulses for the purpose of probing if an x-ray imaging sensor identifiedby the imaging system used in the imaging event would be located withinan operating range of the power transmission link, and whereby as aresponse to said pulse a signal is transmitted from such x-ray imagingsensor including its identifier, whereby as a response to thisidentifying signal of the transmitter and the receiver of the powertransmission link being located within the operating range of thetransmission link, the status of the transmission link is changed toREADY mode, and the sensor is activated ready for imaging.
 13. A methodaccording to claim 12, wherein operation of the x-ray imaging sensor isso controlled that the x-ray imaging sensor activates ready for imagingonly when being located within an operating range of said wireless powertransmission link or wherein energy transmission to the x-ray imagingsensor or the power consumption of the x-ray imaging sensor is adjustedduring the imaging event.
 14. A method according claim 12, whereinenergy will be started to be transmitted to the x-ray imaging sensor inconnection with the imaging event as a response to a signal according towhich the charge level of a capacitor or other component capable ofstoring energy pertaining to the sensor electronics is below a presetlimit value for the charge level or wherein the supply of energy to thex-ray imaging sensor is ended as a response to a signal according towhich the charge level of a capacitor or other component capable ofstoring energy pertaining to the sensor electronics has reached a presetlimit value.
 15. A method according to claim 12, wherein during anactual exposure pertaining to the imaging event, or during a time whenimage data is being read from a detector arranged to the imaging sensorto a memory arranged to the x-ray imaging sensor or while image data isbeing transmitted from the x-ray imaging sensor, the x-ray imagingsensor is supplied with only a little or no energy at all via said powertransmission link.
 16. A method according to claim 12, wherein aninductive link is used as said wireless transmission link arranged tofunction at least as a wireless power transmission link.
 17. A methodaccording to claim 16, wherein a magnetic field produced by an inductivetransmitter of said wireless transmission link arranged to function atleast as a wireless power transmission link is utilized in positioningthe x-ray imaging sensor with respect to an X-ray beam used in theimaging event by utilising data received from a coil of an inductivereceiver arranged to the x-ray imaging sensor, or from one or more othercoils arranged to the x-ray imaging sensor for this purpose.
 18. Amethod according to claim 12, wherein said wireless transmission linkarranged to function at least as a wireless power transmission link isalso used for transmitting data, such as sensor control data.
 19. Amethod according to claim 12, wherein said wireless transmission linkarranged to function at least as a wireless power transmission link isarranged in functional connection with a radiation source used in theimaging event so that operation of the radiation source is arranged todepend on a signal which, as a response to a signal sent from thewireless transmission link arranged to function at least as a wirelesspower transmission link indicates that the x-ray imaging sensor,identified by the imaging system and comprising a receiver of said powertransmission link, is located within the operating range of the wirelesspower transmission link.